High-temperature cobalt base alloys



United States Patent HIGH-TEMPERATURE COBALT .BASE ALLOYS -WilliamCharles Clarke, Jr., Dnndalk, -Md., assignorfto ArmcoSteel Corporation,a corporation of Ohio No Drawing. Application SeptemberZS, 1949, SerialNo. 118,453

8 Claims. (CL' 75-134) Thisinvention relatesgencrallyto high temperaturealloys, and more particularly to alloys having .a high. degreeofresistance to the combined effects of heat and stress.

An object of my invention is the provision of durable and reliable hightemperature alloys.

Another object of my invention is that of providinghigh temperaturealloys which are highly capable of withstanding the combined .andcontinuedeffects of elevated temperatures and stress.

A further object of this invention is the provision of alloys. of'thecharacter indicated whichuare amenable to such operations as forging andhot rolling.

.Other. objects .of. my invention. impart .will. the. obvious .and inpart pointed out more fully hereinafter.

The invention, accordingly, consists incthe combination ofvelements,composition of materials, in the prod- ..ucts, articles and.manufactures, and in the several method steps and-the relation of each.of thesame to one or more .of the others as described herein, thescopeof the appplication-of which is indicated in thefollowing claims.

As conducive ate a clearer understanding of certain features of myinventiongit may 'benoted at this point that many alloys, andarticlesand products made of alloy metal, :arentoday in demand for hightemperature use. infrequently-occurs that metal products in this generalcategory are needed for use at temperatures above. about 1000 P. whichincidentally assure that .the .metal will be intenselyhot, this usesometimes over a long.and.continued periodaof time; There are occasionstoo wherethe alloy products, in'view of.the;particular use at hand, aresubjected to load andstressunderthe prevailing conditions of intenseheat.

.A variety of alloys-which perhaps rightfully belong in the lowtemperature class are highly susceptible to the development of surfacescale or heat scale when subject- .ed to intense heat. Of evengreatervconsequencelin. cer tain instances, heat causes many of-these;ealloys to--'*be- .come so weak thathigh temperature use isout=of2t-he .question. .The alloys very often. are susceptible to ,creepunder'load, especially while hot, and are furthennnreliable forthereason of ensuing rupture.

.Even many 0 the heretofore known high temperature alloys are extremelylimited. in utility forsuch.reasons -.as having a very marked tendencytoWard-tcreepand stress rupture while intensely heated. Inotherinstanceasome of the conventionalhigh temperatureproductsareobjectionable because of. having very low resistanceto the developmentof heat scale while. heated in the high'temperature range. The alloymetal often is of a kind which aiiordslittle if any resistance tocorrosion as'inhot-corrosive atmospheres such as might surround use in.certain high temperature equipment.

, So. many of the conventional high temperature; alloys are notoriouslydiflicult to work,.as-bytforgingpand hot rolling. For this reason, theyare less in demand for.

reduction to particular form for producingxwrought prod- .-ucts.andarticles. Thiscondition existsithough working is often regarded as beingimportant for producing a high temperature product or article.

An. outstanding object of my invention accordinglyis 'the provisio-n-ofhigh temperature alloysand wrought products and articles of thesame-which reliably resist corrosion andthe development 'of' heat scaleand which have "highlyfavorable creep and stress ruptureproperties inhigh temperatureuse.

Referring. 'now 'morer particularly toithe practice of my invention, .1provide 'high temperature cobalt base..alloys which :in containingcertain elements in critical amounts.inuadditionuto'sthe.cobalt, notonly-have good 5 hot-working:properties,high strength, andhighlyfavorable-resistance:.to: creepcand stress rupture underv intense:heatgbut are:furtherccharacterized by resistance to corrosion and bysubstantial freedom from heat scale. develcopment when in: high.temperature use. These 'alloys' in 0 accordance with :my inventioncontain approximately 12% :to 25% :chromium, 1.5% to.3.5% molybdenum,.2i5% x'to ;4.0% vcopper, carbon inamounts up'to about 0.35%, and theremainder substantially cobalt. Iron .usually is:anelementxpresent-in.thealloy composition, 15 this 'being. inquantities-.upto about 10% either as an impurity orotherwise. My alloycomposition preferably :includes nickel insubstantial amounts up toabout 16%, but on occasionsrnickel may be entirely or substantiallyabsent. Among;otheruconstituents which preferably are 20 in the alloyare upitoabout 3% total titanium and/or .columbium. 'ITPIEIECIxtozintroduce efiective quantities of bothrof the latter for: togetherthey have an especially advantageouseefiect. upon the'high temperatureproperties. There ares-instances though where I provide the ralloys-withouteithertitanium or columbium, as -where theimmedia-teEh-igh.temperature needs are successfully satisfied withoutntheadd-ition. Onlysmall. quantities of suche'eiements .as;manganese, silicon, sulphur andphos- .phorus: usually are in thexalloys, these preferably being-withzthe manganesein quantities ranging up to about2%,"thesiliconranging:upto about 1.5 and the sulphur; andphosphorusa-each not exceeding about 0.04%.

Myncoha-lt base: alloys; derive beneficial high temperature effects.from :the cobalt constituent. Also, the 5 amountsiofChromium:.and-'other elements used are re- :garded.zasnbeingccritioal.With any appreciable lowering .ofwthevchromiumcontent to outsidetherange hereinbeforernoted, scaling. resistance and general corrosionresis-ta-ncev of ithe alloy suffer, and with appreciable in- .creasebeyond the range, hot working difiiculties appear, the :alloyfurthertending'to lose: ductilityin high temperature use. :In general, Ifindthat carbon in exwCCSS ofiia-hout 0.36% is not favorable. 'Where theamounts .of copper; and molybdenum in my'alloys are appreciably lowered.to-outside thealowends'of the ranges given here- .inbefore'foritheseelements,-the high temperature load- .carryingcapacity decreases, orwhere the amounts appreciablyexceed the-upper limits of the ranges, thehot work-mg properties'suifer. Too rnuch molybdenum also.seems.to.impair=scaling resistance. If-nickel is used at .alliin my.alloy, I :keep the nickelbelow about 15% and ,preferably;below-about.l0% for best stress rupture prop- .ertres.'Onzthoseroccasions :where one or 'both'elementsrofrthetgroup.consisting-of titanium and columbium are 'inr'the-alloy, Ifindt-hat best'advantages are had by using nabout up to 8% totaltitanium and/or columbium. 'Largeramounts seem: tozdecrease. the stressrupture properties. Where manganese is in. excessof. about 2% and'silicon'more tha-n about 1.5%, this is detrimental tothe hot-workingproperties.

My high temperature .alloys, especially where the .rnanganese, silicon,sulphur and phosphorus are within .the,percentage.ranges just noted, areamenable to hot workingas byforgingx-and hot'rolling. I, therefore, fre-.q.uently.resortt-to-such: operations as hot Working inproducing.wroughtproiducts andarticles of. the alloy metal, as forexample turbine .parts such as wheels, rotors, blades,"buclcetsornozzles. :Among other high tempera- :turezproducts and articles whichlproduce of the alloy emetal'are supercharger pa-rts,. chemical equipmentparts, tubesfor any or" a variety-of uses such asfor carrying hightemperaturefluids-under pressure. Still furthersexamples of my hightemperature alloy. articles are bolts,

rivets-and fasteners. The-products and articles of manufactureare'strong, durable and reliable- They resist creep and stress rupture.suchas attemperatures ranging fromrabout .1000" .F. to 19.00 F. andwhileeither in- ,termittently.or.continuo.usly.under mechanical stressor load. .Themetal resists-form.ing.heat-scale nnderathe conditions ofintense heat and possesses a valuable degree of corrosion resistance.

In certain instances, I provide products of my cobalt base alloy in suchform as sheet, strip, wire, rods, or the like, which are readily usefulfor fabrication as by cutting, punching or bending into shape, orwelding as by means of oxy-acetylene or arc welding equipment. SometimesI use the sheet, wire, or the like directly in high temperatureapplications without appreciable fabrication.

The cobalt base alloy articles and products which I provide often areuseful without particular heat treatment or after annealing, and thusare often so used. I achieve a remarkable increase though in the hightemperature load-carrying ability by employing a heat treatment in thenature of an annealing and precipitation treatment. In the annealingoperation, I heat the alloy metal to a sufficiently high temperature andfor long enough time to put at least part of the copper, and at leastsome of the titanium and columbium when present, into solid solution.Where desired, advantage is taken of annealing temperatures to achievehot working or other operations for producing my products and articlesof the metal. A preferred temperature range for annealing is that ofabout 2050 F. to 2250" F.

After the annealing and before precipitation heat treatment, I quenchthe cobalt base alloy metal preferably to about room temperature, this,for example, by using air, oil or water as the quenching medium. Bysubsequently heating the quenched metal preferably to Within atemperature range of about 1000 F. to 1400 F. and by maintaining thesame at temperature for long enough time, a critically finely dividedprecipitate is believed to come out in the metal lattice along the slipplanes in the matrix. The copper is thought to precipitate in fine form,or possibly as an intermetallic compound including one or more of thegroup consisting of nickel, titanium or columbium, depending upon whichif any of the nickel, titanium and columbium are present in the alloycomposition. Although not immediately visible with the ordinary lightmicroscope, the precipitates become visible after a very long period oftime at high temperatures is allowed for coalescing. When titaniumand/or columbium are present in the alloy, some portion thereof isthought to come out in the form of carbides. Regardless of theory,however, I find that my high temperature alloys, and articles andproducts thereof, have excellent properties. Upon quenching or coolingthe metal as in air from the precipitation treating temperature, I findthat it has a fine grain structure and is further characterized byenhanced load-carrying capacity in view of the precipitation treatment.I often work the metal in this heat-treated condition, or subject thesame to fabricating and finishing operations, thus providing hightemperature products or articles. During high temperature use of thecobalt base alloy, the precipitates remain critically dispersed,uncoalesced and effective against creep and stress rupture, for longperiods of time. Any heating of the metal to as high as solutiontemperature, of course, tends to put the precipitates back intosolution.

For optimum results, I provide cobalt base alloys of the characterindicated, but which more specifically contain approximately 12% to 25%chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper, 0.08% to 0.20%carbon, and the remainder substantially cobalt. Should nickel be used inthe alloy composition, the amounts of this element preferably range upto about maximum. I prefer to use quantities of both titanium andcolumbium in the alloy, but, on occasions, either or both are omitted.Where used, the titanium ranges in amount up to about 0.35% and thecolumbium up to about 0.70%, alone or together. Iron usually is presentin the alloy in permissible amounts up to about 10%. Where manganese,silicon, sulphur and phosphorus are in the alloy, as usually is thecase, these preferably are with the manganese in quantities ranging upto about 2%, the silicon ranging up to about 1.5 and (ghg/jfsyulphur andphosphorus each not exceeding about A few examples of the hightemperature cobalt base alloys which I provide are noted in Table I. Inthis, it will be observed that Alloys A, B and C respectively haveincreased carbon contents within the permissible carbon range. Also, itwill be seen that the Alloy B has a higher nickel content and a lowerchromium content as compared with either Alloy A or Alloy C.

TABLE I Cobalt base alloys Alloy A, Alloy 13, Alloy 0,

Percent Percent Percent Carbon 0. 11 0. 23 0.30 Chromium 19. 25 16. 3919.00 Molybdenunr- 1. 92 1. 2. 25 Copper 3. 19 3. 08 3. 25 Nickel"... 5.33 15. 40 5.00 Titanium 0. 17 0. 23 0. 20 Columbim 0. 56 0. 53 0. 50Manganese 0. 86 Low 0. 50 Silicon 0.31 0. 55 0. 60 Sulphur 0. 029 0.012Low Phosphorus. 0.02 018 0. 02 Cobalt c 58. 7 52. 8 58. 0 Iron Bal. Bal.Bal.

The several alloys identified in Table I all were subjected to annealingat about 2250 F. for one-half hour, followed by quenching in water andprecipitation heat treatment at about 1350 F. for five hours. The alloysthen were given stress rupture tests, the conditions and results ofwhich appear in Table II.

TABLE II Stress rupture tests of Alloys A, B and C Test Load Time forElong. Bed. of A Temp., S i Rupture (2 per-) Area y F. (hrs.) eent(percent) 1, 500 30, 000 40 8. 1 26.0 1, 500 25, 000 239 6. 5 7. 0 A 1,500 21, 500 492 6. 0 8. 2 1,500 20,000 1, 281 4. 0 2. 5 1, 700 10, 000183 4. 3 3. 3 1, 700 7, 500 532 2. 5 1. 0 1, 500 28, 000 44 9. 0 13. 2 B1,500 25,000 116 4. 0 6. 0 1, 500 23,000 162 4. 3 4. 5 C 1,500 30, 00036 2.0 1.0 1, 500 24, 000 70 1. 0 1.0

My cobalt base alloys have many vaulable high temperature properties,including resistance to stress rupture whether or not the alloys orproducts and articles thereof are in the precipitation heat-treatedcondition. The precipitation heat treatment though enhances a number ofthe properties. Despite the high temperature properties, my cobalt basealloys are capable of reduction as by forging and hot rolling and offabrication in a simple, direct and economical manner by virtue of theinherent ease of working. In view of the excellent working properties, Ioften resort to the production of wrought articles and products of themetal. I find too, though, that my high temperature alloys arethoroughly amenable to casting or molding as in a fixed mold orcentrifugally to desired form. Because of this, I often provide casthigh temperature products and articles of the alloy metal.

Thus it will be seen that there are provided in my invention cobalt basealloys, and products and articles thereof, in which the various objectsnoted together with many thoroughly practical advantages aresuccessfully achieved. It will be seen that the metal is strong, durableand tough, corrosion-resistant and heat-resistant and serves well athigh temperatures over long periods of time under any of many conditionsof actual practical use.

As many possible embodiments may be made of my invention and as manychanges may be made in the embodiment hereinbefore set forth, it will beunderstood that all matter described herein is to be interpreted asillustrative and not as a limitation.

I claim:

1. High temperature cobalt alloy having good hot working properties andgreat high temperature strength and resistance to creep, consisting ofabout 12% to 25 chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper,manganese up to about 2%, silicon up to 1.5%, carbon up to about 0.35%,and the remainder cobalt.

2. High temperature cobalt alloy having good hot working properties andgreat high temperature strength and resistance to creep, consisting ofabout 12% to 25% chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper,nickel up to about 16%, carbon up to about 0.35 up to about 3% in totalamount of at least one element of the group consisting of titanium andcolumbium, manganese in quantities up to about 2%, silicon in quantitiesup to 1.5 and the remainder cobalt.

3. High temperature cobalt alloy having good hot working properties andgreat high temperature strength and resistance to creep, consisting ofabout 12% to 25% chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper,manganese up to about 2%, silicon up to about 1.5%, from about 0.08% to0.20% carbon, at least one element of the group consisting of titaniumup to about 0.35% and columbium up to about 0.70%, and the remaindercobalt.

4. High temperature cobalt alloy having good hot working properties andgreat high temperature strength and resistance to creep, consisting ofabout 12% to 25 chromium, 1.5% to 3.5% molybdenum, 2.5% to 4.0% copper,nickel 5% up to about 16%, manganese up to about 2%, silicon up to about1.5%, from about 0.08% to 0.20% carbon, at least one element of thegroup consisting of titanium up to about 0.35% and columbium up to about0.70%, and the remainder cobalt.

5. High temperature cobalt alloy having good hot working properties andgreat strength and great resistance to creep at high temperatures,consisting of about 12% to 25% chromium, 1.5% to 3.5% molybdenum, 2.5 to4.0% copper, manganese up to about 2%, silicon up to about 1.5%, from0.08% to 0.20% carbon, up to about 0.35% titanium, columbium up to0.70%, up to about 10% iron, and the remainder cobalt.

6. High temperature cobalt alloy having good hot working properties andgreat strength and great resistance to creep at high temperatures,consisting of in approximate amount 0.08% to 0.20% carbon, 19% chromium,2.25% molybdenum, 3.25% copper, 5% nickel, manganese up to about 2%,silicon up to about 1.5%, titanium up to about 0.35%, columbium up toabout 0.70%, and the remainder cobalt.

7. High temperature cobalt alloy wrought metal arti- Cir cles orproducts having great strength and great resistance to creep while hot,said articles or products consisting of about 12% to 25 chromium, 1.5%to 3.5% molybdenum, 2.5% to 4.0% copper, manganese up to 2%, silicon upto 1.5%, carbon up to about 0.35%, nickel up to about 16%, iron up toabout 10%, and the remainder at least about 52.8% cobalt.

8. High temperature cobalt base alloy wrought metal articles or productshaving great strength and great resistance to creep while hot, saidarticles or products consisting of about 12% to 25% chromium, 1.5% to3.5% molybdenum, 2.5% to 4.0% copper, manganese up to 2%, silicon up to1.5%, carbon up to about 0.35%, titanium and columbium up to 3% total,nickel up to about 16%, iron up to about 10%, and the remainder at leastabout 52.8% cobalt.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,115,239 Parr Oct. 27, 1914 1,587,992 Apotzley et al. June 8,1926 1,685,570 Masing et al Sept. 25, 1928 1,945,679 Corson Feb. 6, 19342,072,911 Touceda Mar. 9, 1937 2,081,392 Touceda May 25, 1937 2,108,051Egeberg et al. Feb. 15, 1938 2,246,078 Rohn et al. June 17, 19412,309,136 Neiman Jan. 26, 1943 2,495,063 Hood et al. Jan. 17, 19502,509,800 Blackwood May 30, 1950 2,509,801 Blackwood May 30, 19502,536,034 Clarke Jan. 2, 1951 FOREIGN PATENTS Number Country Date832,391 France June 27, 1938

1. HIGH TEMPERATURE COBALT ALLOY HAVING GOOD HOT WORKING PROPERTIES ANDGREAT HIGH TEMPERATURE STRENGTH AND RESISTANCE TO CREEP, CONSISTING OFABOUT 12% TO 25% CHROMIUM, 1.5% TO 3.5% MOLYBDENUM, 2.5% TO 4.0% COPPER,MANGANESE UP TO ABOUT 2%, SILICON UP TO 1.5%, CARBON UP TO ABOUT 0.35%,AND THE REMAINDER COBALT.